Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 191741
AFDBTV

AREA FORECAST DISCUSSION
National Weather Service Burlington VT
1241 PM EST Sat Jan 19 2019

.SYNOPSIS...
A major winter storm is on tap for the North Country tonight through
Sunday as low pressure over the southern Plains this morning tracks
through the the Tennessee Valley today and up the East Coast Sunday.
Steady snow will develop across the region late this afternoon and
evening, and become heavy at times tonight into Sunday morning.
Snowfall rates of 1 to 2 inches per hour are possible, making for
hazardous travel. As low pressure departs to our east across the
Gulf of Maine and Canadian Maritimes, blowing snow will increase
throughout the day Sunday as north winds increase. Frigid
temperatures and very low wind chills are expected in the wake of
the storm for the Sunday night through Monday night period.
Temperatures will moderate back into the teens on Tuesday, and into
the low to mid 30s for Wednesday of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 943 AM EST Saturday...Strong sfc anticyclone anchored
across swrn Quebec this morning. Arctic air continues to filter
in from sern Ontario and srn Quebec on northerly winds 5-10mph.
At 1430Z, temperatures are hovering near zero in the BTV area,
and closer to -5F near the intl border with dewpoints in the
teens below zero. Widespread wind chills 10 to 20 below and mid-
upper level cloud deck will make for very cold remainder of the
daylight hrs areawide. Mosaic reflectivity already showing
tendency toward mesoscale banding along the I-90 corridor into
srn VT with strong 850-700mb frontal zone near our southern CWA
border. Added in snow flurries next several hours across
Rutland/Windsor counties and parts of the nrn Adirondacks to
account for this mesoscale forcing axis well in advance of the
sfc low over the lower Ohio Valley. Everything else remains
consistent with previous fcst.

Previous Discussion...Really only noise level changes made to
the previous forecast with very good model consistency
persisting and no changes made to current winter weather
headlines. Early morning water vapor shows our impending winter
storm across the southern plains with several lines of
convection and lightning noted across TX/AR/LA/MS. Overall track
of the system today through Sunday remains the same moving
east-northeast into the Tennessee Valley this afternoon, to
around D.C. by 12Z Sunday, and eventually into the Gulf of Maine
by 00Z Monday. Ahead of system, quiet and cold conditions will
be in place across the North Country this morning with temps in
the single digits and teens as high pressure over James Bay
filters southward into the region. Some concern remains across
northern areas where drier/arctic air will be in place when snow
arrives later this afternoon and evening, and this is shown
well in the NAM low level RH fields which don`t fully saturate
until later tonight into Sunday morning. As such, we continue to
highlight a sharp gradient in the snow totals, especially
across the St. Lawrence Valley into the northwest Adirondacks.
On the flip side, across central/southern Vermont, we continue
to see the potential for strong frontogenetic forcing in the
850-700mb layer late tonight through Sunday morning, where
within a mesoscale band we could see 1-2"/hr snowfall rates from
around 06-15Z Sunday. All that said, only minor changes were
made to the storm total snowfall amounts with a general 6-12"
across northern New York, least in the St. Lawrence Valley, and
10-18" across Vermont with the lowest totals near the Canadian
border.

Additional threats during the storm will be cold temperatures and
winds. Temps won`t budge out of the single digits north to low teens
south through the period with just some slight cooling across the
St. Lawrence Valley tonight into the single digits below zero. Add
in some increasing northerly winds Sunday in the 15 to 25 mph range
and gusts to 35 mph in the Champlain Valley, and we`ll be looking at
areas of blowing snow and wind chill values of -5F to -20F.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 415 PM EST Friday...Dangerously cold wind chill expected Sunday
Night into Monday morning with values between -20 and -40 below
zero. Areas of blowing and drifting snow continue into Monday.

The combination of departing 988mb low pres over eastern Maine and
building 1038mb high pres will create brisk northwest winds and
bitterly cold wind chills Sunday Night into Monday, as 925mb temps
drop btwn -25c and -30c. Expect wind chill values btwn -20 and -40
below across the entire North Country, with the core of the coldest
values btwn Midnight and 10 AM Monday. Wind chill highlights will be
needed for this time period. Lows range from -5f to -20f overnight
with highs on Monday +5f to -10f depending upon location.

Synoptic setup shows deepening and closing off 5h circulation across
western/central NY, while sfc low pres moves into the Canadian
Maritimes. This creates north/northwest 925mb to 850mb upslope flow
of 35 to 45 knots, as deeper 925mb to 700mb rh rotates back across
our northern and central CWA Sunday Night into Monday. My experience
tells me we low level caa, upslope flow, and lingering moisture with
closing off system its going to take awhile to shut down the snow
machine, especially eastern CPV and northern/central Green
Mountains. The meso-scale setup is very interesting, as moderate to
extreme instability will be present off Lake Champlain as very cold
air moves over relatively warmer waters, while north/northwest flow
will enhance low level convergence on eastern side. BTV4km shows
strong, but shallow lift thru 15z Monday from cpv convergence on
brisk northerly winds.  Froude numbers show strongly blocked flow
with values >0.50, supporting additional snowfall. The big question,
given the extremely cold thermal profiles and snow growth layer near
the sfc, what are the snow ratio`s? My initial thoughts it will be
needles with very small flake size, but reduce visibilities in the 1
to 2sm range across the western slopes/northern dacks and eastern
cpv thru 18z Monday. Have noted 00z BTV 4km shows additional qpf of
up to 0.10 at BTV from 00z Monday thru 18z with model progged snow
ratio`s of 25 to 30 to 1, which would support an additional 2 to 4
inches locally. For now, I have increased pops into the likely/cat
range with additional snowfall of 1 to 3 inches. Meanwhile, away
from the upslope snow showers and cpv convergence, lingering
flurries and light snow shower activity will persist, but
accumulations will be limited.

Monday night 1039mb high pres builds toward northern NY and winds
should gradually diminish toward 12z Tues. If winds decouple with
fresh snow pack and clear skies, expect temps to quickly fall toward
sunrise. Crntly have -10f to -25f, but some colder sites in the
southern SLV/dacks could be near -30f, if winds decouple.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 240 PM EST Friday...Active period of weather continues
with next system arriving on Weds, with the potential for an
additional wave developing along sharp boundary on Thursday into
Friday. This period is highlighted by plenty of uncertainty
with regards to large scale synoptic pattern and associated low
level thermal profiles. Models in decent agreement with a period
of waa snow on Weds, with strong 850mb jet of 50 to 60 knots,
producing some localized shadowing in the cpv. Expect a general
1 to 3 inches for this event with localized higher amounts in
the high peaks and northern Greens. Initially thermal profiles
are cold enough for all snow, but warm just enough toward the
end for maybe a light mix, especially western dacks and southern
CPV.

Overall pattern for late week shows deepening mid/upper level trof
across the central conus, while potent short wave energy rounds base
and enhances sfc low pres across the se conus. This general idea
looks reasonable, but uncertainty remains with the system tracking
either to our west or along the coast. GFS/FV3 and CMC show a more
eastern track and cooler, while UKMET is the western outlier and the
ecmwf is the eastern outlier. For now have utilized superblend
guidance and will mention high chance/low likely with thermal
profiles supporting mostly snow. Will continue to fine tune the
forecast over the next couple of days. Otherwise, temps warm into
the mid 20s to mid 30s on Weds, before cooling back below normal by
the end of the week.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Through 18Z Sunday...VFR conditions this afternoon will give
way to widespread MVFR-IFR conditions as slight snow moves into
the region from the southwest after 22Z. Conditions will to
worsen after 06Z as heavier bands of snow move in bringing
widespread LIFR conditions throughout the overnight hours. By
morning, snow begins to lighten but northerly winds increase to
10-20 knots and with that blowing snow conditions are expect at
most terminals with after 15Z, with RUT seeing it much earlier
as they will see an easterly wind after 06Z.

Outlook...

Sunday Night: Mainly VFR, with areas MVFR possible. Chance SHSN,
Areas BS.
Martin Luther King Jr Day: Mainly VFR, with local MVFR possible.
Chance SHSN.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. Chance SHSN.
Wednesday: Mainly MVFR and IFR, with areas VFR possible. Likely
SHSN, Likely SHRA.
Wednesday Night: Mainly MVFR, with local IFR possible. Chance
SHSN.
Thursday: MVFR/IFR conditions possible. Chance SHSN.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Storm Warning from 4 PM this afternoon to 4 PM EST
     Sunday for VTZ001>012-016>019.
NY...Winter Storm Warning from 4 PM this afternoon to 4 PM EST
     Sunday for NYZ028>031-034-035.
     Winter Weather Advisory from 4 PM this afternoon to 4 PM EST
     Sunday for NYZ026-027-087.

&&

$$
SYNOPSIS...Lahiff
NEAR TERM...Banacos/Lahiff
SHORT TERM...Taber
LONG TERM...Taber
AVIATION...Verasamy


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